It has long been known that hydrophilic coatings with low friction (coefficient of friction of 0.3 or less) are useful for a variety of medical devices such as catheters, catheter introducers and the like. When low friction surfaces are used, the devices, upon introduction into the body, slide easily with arteries, veins, cannula and other body orifices and passageways. There have been a wide variety of methods used to provide the surfaces desired. In some cases the material of the catheter or medical device is formed of a material having good anti-friction properties such as poly(tetrafluoroethylene) or other plastics which tend to avoid abrasion with the body. However, in many cases the selection of materials does not provide the anti-slip properties desired in conjunction with other desirable properties for the particular medical device.
The art has recognized that polymer surfaces can be provided with hydrophilic coatings formed from combinations of isocyanate, polyurethane and polyvinylpyrrolidone (PVP).
For example, U.S. Pat. No. 4,642,267 discloses a coating which is a simple blend of thermoplastic polyurethane and PVP. When deposited on a substrate and dried, no reactions occur. The coating does not bond to the plastic substrate, and can readily be redissolved in a solvent. Furthermore, the PVP is only lightly complexed, thus allowing the coatings to become generally soft and readily removed when wet.
The present invention, in contrast, is a crosslinked system, and thus more tightly complexes the PVP. Furthermore, some reaction may occur between the isocyanate and the substrate to improve adhesion.
The prior art coatings using PVP typically rely on a 2 step, 2 coating process, usually involving a primer coat of isocyanate or isocyanate/polymer blend which is dried, followed by a second coat containing PVP, a blend of PVP and another polymer, or another hydrophilic polymer such as poly(ethylene oxide). The 2 coatings, one superimposed on the other, are then baked to effect a cure. Several disadvantages to this process exist:
1. The exact ratio of primer material to PVP is difficult to control, as it relies on whatever amounts of primer and PVP happen to be deposited by the wet film during the respective dip coating steps. PA1 2. The primer may begin to redissolve in the second coating solution, causing some loss of primer, and further resulting in difficulty in controlling the primer/PVP ratio. PA1 3. Additional facilities and time are needed for coating with a 2 step process, as compared to a 1 step process. PA1 1. A high molecular weight polyvinylpyrrolidone (PVP), or a blend of two or more such PVP products. PA1 2. A polyhydroxy species or polyol containing at least 2 hydroxyl groups per molecule, or a blend of two or more such polyols. PA1 3. An isocyanate prepolymer or monomer containing at least 2 NCO groups per molecule, or a blend of two or more such isocyanates. PA1 4. A solvent or blend of solvents suitable for dissolving components 1-3, which does not significantly react with the components. PA1 1. The present coatings can be formulated over a wide range of properties such as lubricity, durability, adhesion to various surfaces, etc., because the exact composition of the polyurethane -PVP complex can be tailored to the desired result, and particular substrate and end-use application by selecting the specific isocyanate and polyol combination from a wide range of products available commercially. PA1 2. The ratio of polyurethane (total mass of isocyanate plus polyol) to PVP can be varied exactly during preparation of the coating solution.
Prior patents have suggested applying solutions of polyvinylpyrrolidone with isocyanate and/or polyurethane in multi-step operations. These coatings often lack good durability. For example, U.S. Pat. No. 4,585,666 to Lambert discloses medical devices having hydrophilic coatings formed from an isocyanate layer overcoated with a polyvinylpyrrolidone layer. However, such coatings are of polyurea materials formed from a first solution of an isocyanate being applied to a base, the solvent then evaporated, followed by a second solution application of a polyvinylpyrrolidone, in turn followed by evaporation of the solvent. Cure is effected by baking, in the presence of moisture, thus producing a polyurea. This type of application provides polyurea materials which do not have the tenacity of the coatings of the present invention. Additionally, the multistep procedure makes it difficult to tailor properties and values of the final coatings.
In my copending application Ser. No. 512,872, filed Apr. 23, 1990, there are disclosed coatings which are the result of polyurethane linkages in combination with an association of poly(ethylene oxide). Such poly(ethylene oxide) containing coatings are formed using a one-dip process to provide low friction coatings which are abrasion resistant in the body, hydrophilic and lubricious.